DENVER (Reuters) - A psychiatrist who treated accused Colorado theater gunman James Holmes rejected a law enforcement offer to involuntarily confine him for 72 hours after he told her six weeks before the shooting that he fantasized about killing "a lot of people," the Denver Post reported on Wednesday.

Citing an unnamed source, the newspaper said that Holmes made the remark to his therapist, Lynne Fenton, on June 11. But when a University of Colorado police officer asked whether to detain Holmes on a psychiatric hold, Fenton said no. The news was first reported by KMGH 7News and later confirmed by the Post.

A psychiatric hold is usually involuntary hospitalization for mental health evaluation.

Holmes, 24, is accused of opening fire during a midnight screening of the Batman movie "The Dark Knight Rises" in suburban Denver in July, killing 12 people and wounding 58 others.

The former neuroscience graduate student bought a ticket to the blockbuster movie, but left the theater minutes into the film to don a suit of tactical body armor, helmet and gas mask before returning and spraying the unsuspecting crowd with gunfire from multiple weapons, police have said.

An attorney for Fenton could not be reached by Reuters, but has previously said she would not be commenting on media reports about her client.

University police also declined to comment, citing a court-ordered gag order.

The report came on the same day that the University of Colorado released roughly 3,800 emails pertaining to Holmes that shed light on his student life and the reaction of faculty as it became clear one of their own was the suspected gunman.

"He was a grad student here and, it turns out, had a brief romantic relationship with one of the grad students in my program last fall," Larry Hunter, a computational bioscience professor, wrote in a July 20 email. "She, fortunately, it turns out is in India right now. She knows, and is pretty freaked out."

Another faculty member, Angie Ribera, a professor in the neuroscience department, questioned in the hours after the shooting whether the gunman was linked to the university.

"There are several individuals with the name James Holmes. This one is 24 and lives in North Aurora which makes me wonder if this is the one whom we know."

Her e-mail also suggested that Holmes had not been close with the other graduate students in his neuroscience program.

A MAN UNRAVELING

Prosecutors have depicted Holmes as a young man whose once promising academic career was crumbling at the time of the shooting - one of the bloodiest acts of gun violence in the United States in recent years.

He failed oral graduate school board exams in June, and a professor suggested he may not have been a good fit for his competitive program. Holmes then began a voluntary school withdrawal and amassed a weapons arsenal as part of "a detailed and complex" plan to commit mass murder, prosecutors charge.

One email sent by the manager of environmental compliance at the Environmental Health and Safety Department shortly after Holmes was identified as the suspected shooter, confirmed he had access to various chemicals.

Holmes had booby-trapped his apartment, across the street from the Anschutz Medical Campus where he had been a student. It took officials days to disarm the set-up, which they said could have leveled the apartment complex.

"We did see him in the archived files as a lab worker," manager Christina Aguilera wrote on July 20. "If they have an inventory in our file, we can tell what that should have looked like and then we can compare that with what is in the lab now."

University faculty also offered support to students after the shooting, while also repeatedly imploring those who knew Holmes not to divulge information to the press or on social media.

"It appears that the shooter at the Batman premier was one of our students," Cammie Kennedy, the program administrator for the neuroscience program, wrote in an email to students hours after the shooting.

"Students, I am here in my office if you need me," she added. She also asked students to "please NOT post anything on Facebook, Twitter, etc."

Holmes has yet to enter a plea in the case, and prosecutors have not indicated whether they will seek the death penalty. Holmes' lawyers, who analysts have suggested may be laying the groundwork for an insanity defense, have said he suffers from mental illness and sought to get help before the shooting.